Supermolecular Structure Research Articles

Supermolecular structures of recrystallized starches with amylopectin side chains modified by amylosucrase to different chain lengths

Understanding the supermolecular structures of recrystallized starches is imperative to manufacture novel starches with controllable physicochemical properties enabling novel applications. In this study, native amylopectin (AP) from maize was modified to different chain lengths using amylosucrase from Neisseria polysaccharea. Native AP granules showed well-organized lamellar structures with a periodicity of ca. 9.0 nm whereas modified starches formed heterogeneous structures with the average crystallite size ranging from 19.77 to 29.88 nm. Acidic treatments eroded amorphous domains in both native AP granules and modified starch particles, producing nanocrystals composed of double helices. A-type nanocrystals (~40 nm) from native AP granules showed quadrangular shape with an acute angle of ca. 60°, while irregular B-type nanocrystals were observed for the modified starches. Molecular characterizations suggested that the nanocrystals had relatively uniform chain lengths (DP 16.5–25.2), and the helix length (the thickness of nanocrystals) was positively correlated to the thermal stability of starches.

UHMWPE-Based Glass-Fiber Composites Fabricated by FDM. Multiscaling Aspects of Design, Manufacturing and Performance.

The aim of the paper was to improve the functional properties of composites based on ultra-high molecular weight polyethylene (UHMWPE) by loading with reinforcing fibers. It was achieved by designing the optimal composition for its subsequent use as a feedstock for 3D-printing of guides for roller and plate chains, conveyors, etc. As a result, it was experimentally determined that loading UHMWPE with 17% high density polyethylene grafted with VinylTriMethoxySilane (HDPE-g-VTMS) was able to bind 5% glass fillers of different aspect ratios, thereby determining the optimal mechanical and tribological properties of the composites. Further increasing the content of the glass fillers caused a deterioration in their tribological properties due to insufficient adhesion of the extrudable matrix due to the excessive filler loading. A multi-level approach was implemented to design the high-strength anti-friction ‘UHMWPE+17%HDPE-g-VTMS+12%PP’-based composites using computer-aided algorithms. This resulted in the determination of the main parameters that provided their predefined mechanical and tribological properties and enabled the assessment of the possible load-speed conditions for their operation in friction units. The uniform distribution of the fillers in the matrix, the pattern of the formed supermolecular structure and, as a consequence, the mechanical and tribological properties of the composites were achieved by optimizing the values of the main control parameters (the number of processing passes in the extruder and the aspect ratio of the glass fillers).

On finding the zero‐shear‐rate viscosity of polymer melts

AbstractA significant fraction of the experimental works on the rheology of polymer melts include an attempt to find the zero‐shear‐rate viscosity η0. This is done for good reasons, because η0 is a limiting property that depends only on thermodynamic variables and, importantly, the molecular and supermolecular structure of the melt. As with all limiting properties, η0 is impossible to measure directly. Fortunately with many melts, it can be estimated from viscosity measurements at very low shear rates or frequencies, but still remains one of those properties that becomes in the limit very prone to error. The common approach is to use a set of frequency‐ or shear‐rate‐dependent data and extrapolate to find η0. As with any extrapolation, the major question is the function used for the extrapolation. This question is addressed in some detail in this article. The question of which function to use was discarded in favor of using a large sample of 20 equations of many functional forms. This sample of randomly chosen equations was used to generate a set of η0 values, and the statistics of this distribution were examined, in the usual fashion, by description with an analytical probability density function that gives a high probability of being a likely generator of the data. In addition, a weighted average was proposed, where the weighting factor takes into account the quality of the fit. For testing these ideas, the room temperature melts of poly(vinyl isobutyl ether), poly(isobutylene), and poly(dimethyl siloxane) were used. The η0 of the latter was reachable; for the other resins, a falling ball technique was attempted.

Unconventional inorganic precursors determine the growth of metal-organic frameworks

Abstract Crystalline metal-organic frameworks (MOFs) are an emerging type of the hybrid materials with multifunctional inorganic and organic building blocks, which have been applied in a wide range of energy-related and environment-related applications. In this context, a remaining challenge in the systematical syntheses of hierarchically porous MOFs composites is existing to alter supermolecular structure, chemical composition, and versatile functionality. It is generally accepted that the regulation of MOF preparation is of great significance, which is related to the solubility of those starting inorganic components. We learn that there are several possible drawbacks induced by conventional soluble metal precursors in homogeneous reaction conditions, so the increasing research interest in the facile synthesis of MOFs and their derivatives from insoluble metal templates and/or precursors has been ignited in the past decade. In this review, we aim to provide an overview of the facile preparation and usage of MOF materials by using the unconventional inorganic precursors in heterogeneous synthetic conditions, including template types, preparation methods, extension strategies, advantages, limitations and related applications.

Syntheses, crystal structures, thermodynamic and fluorescent properties of dinuclear lanthanide complexes constructed with 2-fluorobenzoic acid and 5,5′-dimethy-2,2′-bipyridine

2-fluorobenzoic acid and 5,5′-dimethy-2,2′-bipyridine were used to construct two novel isostructural lanthanide complexes [Ln(2-FBA)3(5,5′-DM-2,2′-bipy)]2 (Ln = Eu(1), Tb(2); 2-FBA = 2-fluorobenzoate; 5,5′-DM-2,2′-bipy = 5,5′-dimethy-2,2′-bipyridine) by conventional solution method. They were characterized by infrared spectroscopy (IR), elemental analysis and single-crystal X-ray diffraction. The crystal description based on single-crystal X-ray diffraction data revealed that both of the complexes gave the triclinic crystal structure, belonging to the Pī space group. The two complexes were an infinite one-dimensional (1D) chain by hydrogen bonding (C–H…F) interactions to give a 2D supermolecular structure. Additionally, thermal behavior of the complexes was investigated by TG-DSC/FTIR technology in detail. The molar heat capacities of the two complexes in the temperature range of 278.15-423.15 K were determined by a DSC instrument, and their thermodynamic functions (HT-H298.15 K) and (ST-S298.15 K) were calculated. Beyond that, the fluorescence spectra and fluorescence lifetime of the complexes 1 and 2 were also evaluated.

Influence of wood thermal modification on the supermolecular structure of polypropylene composites

AbstractThe thermal modification of wood can be an interesting way of improving adhesion in polymer composites, although the mechanical properties of composites with heat treated wood presented so far in many works arouse much controversy. In this work, effects of thermal modification of wood on the supermolecular structure and morphology of wood/polypropylene composites (WPC) were investigated using X‐ray diffraction, hot stage optical microscopy, and differential scanning calorimetry. A significant impact of the conditions of thermal wood modification on the formation of polymorphic varieties of the polymer matrix has been demonstrated. Furthermore, thermal treatment also affected the nucleation activity of wood, which was confirmed by determined parameters such as, crystal conversion, half crystallization time, and crystallization temperature. In addition, differences in the formation of transcrystalline structures responsible for the level of interfacial adhesion were depicted based on hot stage optical microscopy. Mechanical tests have shown that obtaining the appropriate strength properties of composite materials depends on the selection of appropriate conditions for thermal modification, which determine the supermolecular structure and nucleation activity. The obtained results, not reported so far, are extremely important when designing WPC composite materials with strictly defined physicochemical parameters.

Structural investigation of semicrystalline polymers

This work demonstrates the most widely used characterization methods and techniques of the supermolecular and lamellar structure of semicrystalline polymers. Polarized optical microscopy (POM) equipped with a hot-stage (thermo-optical microscopy, TOM), brightfield microscopy (BF), darkfield microscopy (DF), digital image processing techniques, optical profilometry (OP), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used as investigation techniques. The same iPP grade was used with different sample preparation techniques to compare these methods. The advantages and drawbacks of the sample preparation and investigation methods were discussed. The results show how the introduced techniques could reveal different kinds of information, and it is also shown how the experimental techniques should be matched to the goals of a structural study.

Phase separation and DAXX redistribution contribute to LANA nuclear body and KSHV genome dynamics during latency and reactivation.

Liquid-liquid phase separation (LLPS) can drive formation of diverse and essential macromolecular structures, including those specified by viruses. Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) genomes associate with the viral encoded Latency-Associated Nuclear Antigen (LANA) to form stable nuclear bodies (NBs) during latent infection. Here, we show that LANA-NB formation and KSHV genome conformation involves LLPS. Using LLPS disrupting solvents, we show that LANA-NBs are partially disrupted, while DAXX and PML foci are highly resistant. LLPS disruption altered the LANA-dependent KSHV chromosome conformation but did not stimulate lytic reactivation. We found that LANA-NBs undergo major morphological transformation during KSHV lytic reactivation to form LANA-associated replication compartments encompassing KSHV DNA. DAXX colocalizes with the LANA-NBs during latency but is evicted from the LANA-associated lytic replication compartments. These findings indicate the LANA-NBs are dynamic super-molecular nuclear structures that partly depend on LLPS and undergo morphological transitions corresponding to the different modes of viral replication.

Synthesis and properties of tetraphenylethylene derivatives with different chiral substituents: From helical supermolecular structure to circularly polarized luminescence

Two novel tetraphenylethylene derivatives (denoted as A12-TPE and T12-TPE) were prepared by incorporating different chiral d-gluconic acid substituents into the achiral TPE core. Their aggregation-induced emission (AIE) activity, self-assembly structure and circularly polarized luminescent (CPL) performance were then investigated using various techniques. The results reveal that both A12-TPE and T12-TPE exhibit AIE properties with quantum yields as high as 74.3% and 74.0% respectively. Moreover, due to the synergy effect of steric hindrance of the acetal group and chiral induction of d-gluconic acid, A12-TPE possesses a helical supermolecular structure, which endowed the material with distinct CPL properties. On the contrary, T12-TPE without the acetal group exhibits a lamellar structure rather than a helical structure, and no CPL signal can be observed. The helical supermolecular structure, in combination with the AIE activity and CPL performance of A12-TPE, make it a promising material for fabrication of chiral luminescent devices.

Collagen Fibril Tensile Response Described by a Nonlinear Maxwell Fluid Model

Collagens are a family of proteins and constitute about 35% of the total human proteome. The most abundant collagens form super-molecular structures; the so-called collagen fibrils. Collagen fibrils are the basic structural building blocks that provide mechanical stability to tissues from the nano- to the macroscale. Collagen fibrils are highly hydrated and hence transient deformation mechanisms may contribute to their viscoelasticity. Individual mechanical assessment of collagen fibrils can be achieved either by custom-built instruments or more conveniently by employing atomic force microscopy (AFM). One approach to quantify the viscoelastic behavior of collagen fibrils and estimate their material properties is to find fitting constitutive equations. In this study, we present a constitutive equation considering a nonlinear rheological Maxwell model. The model was fitted on stress-time data from tensile tests conducted on hydrated and partially dehydrated collagen fibrils with AFM. The model describes the nonlinear behavior sufficiently and shows a high quality of fit (R 2 > 0.99). The apparent tensile modulus, estimated by the constitutive equation, is rising with decreasing hydration state of the collagen fibrils, while viscosity seems to be constant, suggesting collagen fibrils mechanically behave as a highly viscous liquid with a high concentration of solid ground substance.

Enzymatic engineering of nanometric cellulose for sustainable polypropylene nanocomposites

In this work, the influence of enzymatic modification on the properties of nanocellulose reinforced polypropylene nanocomposites was investigated in detail. Methods such as high-performance liquid chromatography coupled with a refractometric detector, differential scanning calorimetry, X-ray diffraction, dynamic light scattering, and optical microscopy were used in this study. In addition, the tensile properties of polymer nanocomposites were tested. Enzymatic modification of nanocellulose was carried out using cellulases from microorganisms Trichoderma reesei and Aspergillus sp. (Viscozyme®L). It was found that controlled, enzymatic hydrolysis of nanocellulose resulted in significant changes in the morphology, super molecular structure, as well as nucleating behaviour of transcrystalline structures. Because of the modification, nanocellulose was obtained with an increased amount of the crystallinity phase (70 %) and the content of nanometric particles with a size below 100 nm at the level of about 94 %. In addition, an interesting correlation between kinetic parameters (crystallization temperature, degree of phase conversion, crystallization half times) and creation of different crystal phase of the polymer matrix was established. Composites containing nanocellulose modified in the enzymatic process have been characterized by the presence of a significant amount of additional β-PP polymorph at the level of 40 %, as well as very good nucleation properties, e.g. an increase in the crystallization temperature by 5 °C, a reduction of crystallization half times and induction times of transcrystalline structures by approx. 30 %. Besides, tensile tests of nanocomposites proved that types of enzymatic modification have an important impact on the morphology of nanocellulosic fillers, and as a result, determines the polypropylene nanocomposite’s mechanical performance. It is worth mentioning that the introduction of nanocellulose modified with the Trichoderma reesei enzyme into the polypropylene matrix resulted in the production of composites with a significantly increased value of strength at break 36 MPa and high values ​of elongation at break (over 80 %). Furthermore, the use of specific enzymes enables procurement of a nanocellulose with strictly defined dispersive characteristics that also affects the supermolecular structure of nanocomposites, and consequently the mechanical properties. Depending on the content of individual polymorphs, it is possible to control the flexibility of produced nanocomposite materials.

Mirror-image antiparallel β-sheets organize water molecules into superstructures of opposite chirality

Biomolecular hydration is fundamental to biological functions. Using phase-resolved chiral sum-frequency generation spectroscopy (SFG), we probe molecular architectures and interactions of water molecules around a self-assembling antiparallel β-sheet protein. We find that the phase of the chiroptical response from the O-H stretching vibrational modes of water flips with the absolute chirality of the (l-) or (d-) antiparallel β-sheet. Therefore, we can conclude that the (d-) antiparallel β-sheet organizes water solvent into a chiral supermolecular structure with opposite handedness relative to that of the (l-) antiparallel β-sheet. We use molecular dynamics to characterize the chiral water superstructure at atomic resolution. The results show that the macroscopic chirality of antiparallel β-sheets breaks the symmetry of assemblies of surrounding water molecules. We also calculate the chiral SFG response of water surrounding (l-) and (d-) LK7β to confirm the presence of chiral water structures. Our results offer a different perspective as well as introduce experimental and computational methodologies for elucidating hydration of biomacromolecules. The findings imply potentially important but largely unexplored roles of water solvent in chiral selectivity of biomolecular interactions and the molecular origins of homochirality in the biological world.

Comparison of macro-, micro- and nanomechanical properties of clinically-relevant UHMWPE formulations

We characterized a set of eleven clinically relevant formulations of UHMWPE for total joint replacements. Although their molecular and supermolecular structure were quite similar as evidenced by IR, DSC and SAXS measurements, there were slight differences in their crystallinity (DSC crystallinity ranging from 52 to 61%), which were connected with processing conditions, such as the total radiation dose, thermal treatment and/or addition of biocompatible stabilizers. Mechanical properties were assessed at all length scales, using macroscale compression testing, non-instrumented and instrumented microindentation hardness testing (at loading forces ~500 mN), and nanoindentation hardness testing measured at both higher and lower loading (~4 mN and ~0.6 mN, respectively). In agreement with theoretical predictions, we found linear correlations between UHMWPE crystallinity and its stiffness-related properties (elastic moduli, yield stress, and hardness) at all length scales (macro-, micro- and nanoscale). Detailed statistical evaluation of our dataset showed that the accuracy and precision of the applied methods decreased in the following order: non-instrumented microindentation ≥ instrumented microindentation ≥ macromechanical properties ≥ nanoindentation measured at higher loading forces ≫ nanoindentation measured at lower loading forces. The results confirm that microindentation and nanoindentation at sufficiently high loading forces are reliable methods, suitable for UHMWPE characterization.

Structural evolution of β-iPP with different supermolecular structures during the simultaneous biaxial stretching process

Two different supermolecular structures of β-iPP cast films were used to investigate structural evolution during the simultaneous biaxial stretching process via small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. Based on the mechanical behaviors and porosity variations during the stretching process, it was found that the two samples had different structural evolution modes. During the initial stage of deformation, β-hedrites exhibited violent cavitation behavior in the center region of the hedrites by forming elliptical crazes and expanding, while β-spherulites were more inclined to fragment into blocky crystal structures, which was accompanied by the slippage of these structures. In the later stages of stretching, β-hedrites formed numerous dense regions around the elliptical crazes, which hindered microvoid formation and led to a poor pore size distribution. Conversely, β-spherulites generated abundant microfibrillar structures, and abundant microvoids were formed by directly separating the microfibrils, forming a membrane with a superior pore size distribution. The structural evolution of β-iPP with two different supermolecular structures during the simultaneous biaxial stretching process was studied. The two samples showed different structural evolution modes. β-hedrites exhibited violent cavitation behavior during the initial stage of deformation, but in the late stages of stretching β-hedrites formed numerous dense regions, which hindered microvoid formation and led to a poor pore size distribution. Conversely, β-spherulite generated abundant microfibrillar structures, and abundant microvoids were formed, forming a membrane with a superior pore size distribution.

Exchange Interactions Drive Supramolecular Chiral Induction in Polyaniline (Small Methods 10/2020)

In article number 2000617, Claudio Fontanesi and co-workers study the camphor sulfonic acid induction of chirality on the supermolecular structure of electropolymerized aniline. The emergence of chirality is also associated to spin filtering properties of the chiral polymer, revealed by conducting probe atomic force microscopy in the presence of a magnetic field. Theoretical results suggest that the chiral induction is due to exchange interaction energy.

Buckling and Torsional Instabilities of a Nanoscale Biological Rope Bound to an Elastic Substrate.

Rope-like structures are ubiquitous in Nature. They are supermolecular assemblies of macromolecules responsible for the structural and mechanical integrity of plant and animal tissues. Collagen fibrils with diameters between 50 and 500 nm and their helical supermolecular structure are good examples of such nanoscale biological ropes. Like man-made laid ropes, fibrils are typically loaded in tension, and due to their large aspect ratio, they are, in principle, prone to buckling and torsional instabilities. One way to study buckling of a rigid rod is to attach it to a stretched elastic substrate that is then returned to its original length. In the case of single collagen fibrils, the observed behavior depends on the degree of hydration. By going from buckling in ambient conditions to immersed in a buffer, fibrils go from the well-known sine wave response to a localized behavior reminiscent of the bird-caging of laid ropes. In addition, in ambient conditions, the sine wave response coexists with the formation of loops along the length of the fibrils, as observed for the torsional instability of a twisted filament when tension is decreased. This work provides direct evidence that single collagen fibrils are highly susceptible to axial compression because of their helical supermolecular structure. As a result, mammals that use collagen fibrils as their main load-bearing element in many tissues have evolved mitigating strategies that protect single fibrils from axial compression damage.

Modeling a Microtubule Filaments Mesh Structure from Confocal Microscopy Imaging.

This study introduces a modeling method for a supermolecular structure of microtubules for the development of a force generation material using motor proteins. 3D imaging by confocal laser scanning microscopy (CLSM) was used to obtain 3D volume density data. The density data were then interpreted by a set of cylinders with the general-purpose 3D modeling software Blender, and a 3D network structure of microtubules was constructed. Although motor proteins were not visualized experimentally, they were introduced into the model to simulate pulling of the microtubules toward each other to yield shrinking of the network, resulting in contraction of the artificial muscle. From the successful force generation simulation of the obtained model structure of artificial muscle, the modeling method introduced here could be useful in various studies for potential improvements of this contractile molecular system.

The Effect of Physical-Chemical Nature of UHMWPE and PPS Thermoplastic Matrices on the Formation of Mechanical and Tribological Properties of their Carbon Fiber Filled Composites

The effect of carbon fiber dimensions on mechanical and tribological properties of the composites based on two thermoplastic matrices of different physical-chemical nature (polyphenylene sulfide, PPS, and ultrahigh molecular weight polyethylene, UHMWPE) is compared. It is shown that the supermolecular structure formed by compression sintering of PPS and UHMWPE controls the distribution pattern of carbon fibers in the matrix, which affects the level of tribological properties. The composites on a high-strength PPS-matrix, designed for structural/tribotechnical applications and loaded with short carbon fibers (70 μm), can be fabricated at a high loading degree (40 wt.%), which provides a five-fold increase in wear resistance and a 1.7-fold decrease in friction coefficient. The wear resistance increases due to the formation of a third body consisting of wear debris, which essentially reduces the friction coefficient. Loading the PPS with carbon nanofibers modifies the polymer matrix structure through the dispersion hardening mechanism but does not improve its tribological properties. Adding chopped carbon fibers (with a length of a few millimeters) into the PPS matrix gives rise to substantial hardening but significantly degrades the tribological properties. The UHMWPE composites can be manufactured via filling the matrix with 10 wt.% chopped carbon fibers evenly distributed in it. Carbon nanofibers are thought to be the most efficient fillers for the UHMWPE matrix of a spherulitic supermolecular structure in terms of increasing its wear resistance. They play the role of a solid lubricant medium (wear resistance increases 2.7 times, the friction coefficient is decreased twice). Comparatively long chopped carbon fibers of the millimeter range (2–3 mm) play a reinforcing role in contrast to the short carbon fibers measuring tens and hundreds of micrometers (70, 200 μm). They neither increase the friction coefficient nor result in the abrasive wear of the steel counterpart. The role of interphase adhesion, polymer matrix hardness, its chemical reactivity and supermolecular structure in forming the tribomechanical properties of carbon composites based on thermoplastic matrices of different physical-chemical nature is discussed.

Role of Thermolysin in Catalytic-Controlled Self-Assembly of Fmoc-Dipeptides

In recent years, short peptide self-assembled materials, prepared under the control of the thermolysin catalyst, have been investigated extensively and shown to acquire various morphologies and fun...

Supermolecular Structure of Poly(butylene terephthalate) Fibers Formed with the Addition of Reduced Graphene Oxide.

Nanocomposite fibers based on poly(butylene terephthalate) (PBT) and reduced graphene oxide (rGO) were prepared using a method able to disperse graphene in one step into a polymer matrix. The studies were performed for fibers containing four different concentrations of rGO at different take-up velocities. The supermolecular structures of the fibers at the crystallographic and lamellar levels were examined by means of calorimetric and X-ray scattering methods (DSC, WAXS, and SAXS). It was found that the fiber structure is mainly influenced by the take-up velocity. Fibers spun at low and medium take-up velocities contained a crystalline α-form, whereas the fibers spun at a high take-up velocity contained a smectic mesophase. During annealing, the smectic phase transformed into its α-form. The degree of transformation depended on the rGO content. Reduced graphene mainly hindered the crystallization of PBT by introducing steric obstacles confining the ordering of the macromolecules of PBT.